Summary: One of the major outcomes of the recent sequencing of the Mycobacterium tuberculosis (Mtb) genome was the identification of the multigene families designated PE_PGRS and PE. Since little is known about the expression or function of these genes, we have used the gene Rv1818c (PE_PGRS) and its amino-terminal PE region, as prototypes of the PE_PGRS and PE families, to investigate the function and immunological response to these proteins during experimental tuberculosis. Research studies have provided evidence that PEPGRS proteins are cell surface constituents that have a role in Mtb infection of macrophages and in bacterial-bacterial interactions. PE_PGRS and a PE fragment have been expressed in Mycobacterium smegmatis and these strains demonstrate differences in cell phenotype and colony formation suggesting that they insert into the cell surface. These strains are being used to further characterize the function of these proteins. An M. avium strain which lacks PE_PGRS genes but has PE genes is being used to determine if PE genes alone are expressed. PE_PGRS proteins elicit an antibody response following infection and immunization with DNA vaccine constructs. Recombinant PE and PE_PGRS proteins have been expressed and purified and used in immunoassays to show that the dominant B cell epitope resides in the PGRS domain. Recent studies suggest that the antibody response to PE_PGRS varies over time in vivo. No antibody response to the PE domain has been observed. The PGRS domain also appears to regulate protein stability as determined by the use of GFP fusion proteins and there is some evidence to suggest it may effect antigen presentation of the PE domain and of other mycobacterial proteins. A MHC I reporter system is being used to investigate the role of PE_PGRS proteins in regulating proteosome dependent antigen presentation and the possibility that PE_PGRS proteins aid Mtb in evading host immune recognition. A collaboration with Johns Hopkins University is testing the efficacy of a PE DNA vaccine in the rabbit model for TB.